U.S. patent applications Ser. No. 181,974, filed Aug. 28, 1980 and now abandoned, Ser. No. 295,400, filed Aug. 21, 1981, Ser. No. 478,080 filed Mar. 23, 1983, and Ser. No. 572,678, filed Jan. 20, 1984, all of which, together with Ser. No. 580,742, are owned by the assignee of the present application and are here incorporated by reference, disclose flexible sheet heaters including a pair of longitudinally-extending (typically copper) conductors, and a semi-conductor pattern extending between and electrically connected to the conductors. The heaters there disclosed provide generally superior performance and substantially even heat distribution, and are useful in a wide range of applications.
There are circumstances, however, when it is desirable to provide heating closer to the side edges of the heater than can be accomplished with the heater design shown in the aforementioned applications. It also may be desirable to provide a heater construction which, because it eliminates the need for long copper conductors, is less expensive than the heater design of the aforementioned applications.